A team of scientists from France has recently conducted a simulation study to predict the impact of future epidemic waves of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on the country's healthcare system.
The findings indicate that given the lower vaccine efficacy against the SARS-CoV-2 delta variant, France may face a large epidemic wave infecting 25% of the general population even with a 95% vaccine coverage. This, in turn, could affect the healthcare system in terms of hospital bed occupancy. The study is currently available on the medRxiv* preprint server.
To predict the dynamics of future coronavirus disease 2019 (COVID-19) epidemic waves, several mechanistic models have been developed. However, these models often fail to forecast more than a few weeks ahead as the epidemic dynamics mainly depend on the government-implemented COVID-19 controlling strategies. In addition, social, environmental, and biological factors can influence the accuracy of forecasting.
To avoid these uncertainties, the scientists in the current study have predicted the final size of a future epidemic wave by ignoring detailed epidemiological dynamics. The final epidemic size refers to the proportion of infected individuals in a given population during the epidemic wave. Using this approach, they have estimated the numbers of intensive care unit (ICU) admissions and deaths caused by the epidemic wave.
The scientists initially estimated the final epidemic size and subsequently stratified the data by age, SARS-CoV-2 infection-induced immunity, and COVID-19 vaccine-induced immunity. These stratifications were done because the infection fatality rate strongly depends on age and level of immunity.
Furthermore, to facilitate healthcare workers, they introduced a dedicated software COVimpact to semi-quantitatively estimate the frequency of ICU admissions, deaths, and age-stratified infections at the French departmental, regional, and national levels. The analysis assumed that 95% of the population is fully vaccinated, and the overall vaccine efficacy is 85% against severe disease.
The software has two panels for separately selecting geographical scale and vaccination status. The scientists set the percentage of the vaccinated population separately for three age groups: 12 – 17 years; 18 – 65 years; and >65 years. Then, they manually set the vaccine efficacy by assuming that it does not vary with age.
Based on the semi-quantitative findings, the scientists forecasted that even with extremely high vaccine coverage (95%), a large pandemic wave infecting 25% of France's entire population could cause approximately 20,000 ICU admissions. This corresponds to 280,000 days of ICU bed occupancy, given the assumption that the average duration of an ICU stay is 14 days.
Overall, these estimations indicated that even if the epidemic wave lasts for 2 months, more than 4,600 beds would be occupied by COVID-19 patients, which is more than half of the total ICU capacity.
The study highlights that a large future epidemic wave of COVID-19 that infects 25% of the French population in 2 months can impose a severe burden on the healthcare system regarding ICU bed occupancy. This prediction has been made by assuming that 95% of the French population is fully vaccinated. However, the actual vaccine coverage in France is much lower than 95%.
In the study, the scientists have assumed that the protection induced by natural infection, vaccination, or both only reduces the risk of severe disease but does not affect exposure. They have mentioned that these simplified assumptions should be carefully analyzed while forecasting future epidemic waves for other countries.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.